The Diamondbacks have shut down ace Brandon Webb for three weeks with soreness in his right shoulder. The move means that Webb won't return to a Major League mound before mid-May. He suffered a setback on Friday while warming up in a scheduled bullpen session before the team's game against the Giants. "We really don't know anything right now," manager Bob Melvin said. " ... This is absolutely confusing because he felt good last time out, and all the maintenance stuff leading up to this would suggest he felt good. But once he played catch there was just some tightness in the same spot and, we didn't want to push it any further than that."